Local number portability (LNP) is a service feature for telephone service subscribers that permits a subscriber to retain his/her telephone number while relocating from one subscriber line to another within a local toll area. A problem associated with enabling LNP involves efficiently directing calls to a ported subscriber's new line, which is connected to a Central Office that is not provisioned to serve the ported directory number. A second problem involves the retention of the subscriber's service features throughout the porting process without interruption and/or extensive re-provisioning, and without losing feature continuity.
Many prior art solutions have been proposed to address the problem of how to provide LNP to telephone service subscribers. A few of these are briefly discussed following a description of the telecommunications network in which they are designed to be implemented.
Legacy switched telecommunications networks, as schematically illustrated in FIG. 1 and familiar to those skilled in the art, include Central Offices 10 equipped with Time division multiplexed (TDM) switches 11 that transmit multiple streams of pulse code modulated (PCM) data across a circuit-switched bearer network generally referred to as the public switched telephone network (PSTN) 18. The TDM switches 11 include a central processing unit (CPU), generally referred to as a “Control Module” (CM) 16, a plurality of line interfaces (LIs) 22, a switch fabric 34, and a plurality of digital trunk controllers (DTCs) 30. As is well understood by those skilled in the art, other peripherals may also be supported by the TDM switches 11.
The plurality of LIs 22 are TDM switch peripherals that provide interfaces between subscriber lines 15 and the TDM switches 11. Lis 22 include such devices as line carrier modules (LCMs), well known in the art. Each of the plurality of DTCs 30 are likewise TDM switch peripherals that provide interfaces for inter-switch trunks 19 that interconnect the TDM switches 11. Trunks 19 are devices such as T1 and E1 facilities, also well known in the art.
The CM 16 of a TDM switch 11 controls a connection through the switch fabric 34, between two TDM switch peripherals. The CM 16 is also responsible for call control messaging via a common channel signaling (CCS) network 20. The call control messaging is used to coordinate actions of TDM switches 11 to establish call connection between two subscribers.
The common channel signaling (CCS) network 20 delivers call control messages involved in the set-up, tear-down, and monitoring of call connections. In North America, signaling system 7 (SS7) is generally used for call control messaging. The CCS network 20 routes call control messages between CMs 16 of different TDM switches 11 to control inter-switch calls.
As noted above, several methods for enabling LNP have been proposed. In several prior art methods for providing LNP, ported directory numbers are stored in a database 24 with routing instructions for completing calls to a current location of equipment serving the numbers such as a ported directory number shown at 14. This solution is typified by U.S. Pat. Nos. 5,867,569; 5,598,464; 5,905,724; and 5,949,870. The LNP database 24 may be any network element or subnetwork element of the CCS network 20 that is accessed to retrieve LNP routing information related to subscribers who have ported directory numbers. The LNP database 24 could therefore be a Service Control Point (SCP), a memory associated with a Central Office, or an Intelligent Network (IN) or Advanced Intelligent Network (AIN) device. The content of the LNP database 24 is used to direct call control messages to network switching equipment that serves a ported subscriber's line.
The public switched telephone network (PSTN) is currently in transition and moving toward the use of high-bandwidth broadband networks for performing bearer transport, to augment the circuit-switched PSTN. Broadband networks emulate circuit-switched bearer networks by providing virtual trunking for calls. One example of a new switched telecommunications network configuration using a broadband bearer network is described in Applicant's co-pending U.S. patent application Ser. No. 09/702,776, which was filed on Nov. 1, 2000 and entitled DISTRIBUTED TELEPHONE SERVICE SWITCH AND METHOD OF USING SAME.
Although advances in network technology have been made, none of the known proposals for LNP are ideal, and all known proposals fail to capitalize on new possibilities enabled by the introduction of broadband bearer networks into the PSTN.
There therefore exists a need for an LNP solution that capitalizes on the routing flexibility introduced into the PSTN by the implementation of broadband transport networks for inter-switch trunking.